When you ride your bike at constant velocity (say 5 m/s) you tend to keep your balance far easier than when...

physics/bicycle.balance New

New entry, edited from material collected for the archive and not yet in a released version.

Problem

When you ride your bike at constant velocity (say 5 m/s) you tend to
keep your balance far easier than when you try the same thing at 0
velocity.  How come?  Do the same rules apply for a unicycle?

-- Dirk Remacle (June 1996)

Show solution

The wheels are acting as gyroscopes.  If you let a moving bike tilt to
one side, the front wheel will experience a force twisting it into the
direction of the fall (in the same direction that someone will
instinctively turn the handlebars), which will restore stability.

You can demonstrate this easily by unbolting the front wheel of your
bike, holding it with the axle horizontal in front of you, and get
someone to spin it fairly briskly away from you.  Now tip the wheel to
the right (rotate about a horizontal axis going away from you)...you
will feel a force twisting it right about a vertical axis, too).

> Do the same rules apply for a unicycle?

Yes.  The only time it won't apply is if you're riding a bicycle with
the front wheel locked in one direction (why you'd want to do this, I
have no idea).  The restoring force can't turn the wheel, and you'll
fall over.

-- Richard Balthazor <r.balthazor@sheffield.ac.uk>